The long term goal of this research program is to identify the genes and signaling pathways that control sexual differentiation of social behavior. Sex differences in neurological diseases, normal and abnormal behaviors are well documented, but the mechanisms underlying the differences are not. Many behavioral disorders (i.e. schizophrenia, depression, autism etc.) have one universal symptom; atypical social interactions. Our goal is to understand development of normal social behavior and use this information to reveal novel genetic mutations in patients with behavioral disorders. In the past few years we have established that the androgen receptor (AR) is a major component in the sexual differentiation of social affiliative behaviors in the mouse. This is exciting because the AR has been implicated in sexual differentiation of primates, including humans. We will advance this finding by studying the genetic regulation of sexual differentiation downstream of AR, and we will discover the essential AR target genes. In Aims 1-3 we will validate one potential AR target gene, Calbindin D28k. Calbindin defines a sexually dimorphic cell cluster in the medial preoptic area. In addition, this calcium binding protein has well characterized anti-apoptotic actions in brain, and for these reasons it is very likely a contributor to the sexual differentiation pathway. We will use a number of genetically engineered mice, molecular, genetic and behavioral methods to characterize the relationship between the AR and Calbindin at the level of mRNA and protein. We will also use Calbindin knockout mice to assess the behavioral ramification of the loss of function of this gene. Finally we will conduct Microarray experiments to uncover novel candidate genes that are androgen responsive. The strategy we will pursue delineates the role AR plays in regulation of a gene that is part of a neuroprotection pathway and is likely involved in sexual differentiation. This same strategy can be recycled to identify other AR target genes.